The players are basically arguing that as a matter of principle reporters should not be revealing things which happened behind closed doors. They also brought up the real-world motivation against it: players (like Jeremy Roenick admitted he's done) and teams denying reporters access.

There can be an argument for the latter case, though surely reporters are not unable to hammer the team in the media for the denials in the first place. There are a lot of ethical concerns about a situation where reporters are publishing things they overheard inside the locker room and being denied team/player access: however they are all ethical concerns for the sad sacks of shit in the league, not the journalist per se.